Hi guys, I'm currently using a Core i5 750, Gigabyte P55A-UD3, and 2x2GB G.Skill DDR3 12800. The heatsink used is the Thermalright Ultima 90. IIRC, temperature is hovering in the 28C to 30C range.

Right now speed is at default. Ultimately I would like to do 4ghz on air if possible. However, I know nothing is ever guaranteed so I guess I'll have to raise the clock speed carefully.

IIRC, stock speed is at 2.66ghz. My first goal is to try 3.5ghz. Can someone tell me what settings I should use in the BIOS to increase the chance of hitting 3.5ghz? I would prefer tight timings, but it's not necessary. What voltages should I try using? After overclocking the system, I plan to use Prime95 for stability test and hopefully things will pan out.

+1 for monster. You can drive your cpu at 3.5 with a hand clap. 4Ghz is more a challenge but it's trully possible. For the setting, follow linus and then just get them higher to get to 4Ghz. But! never forget to look at the Intel maximum power for your CPU.

Ok so I did a bit more research on this matter and tried to do an initial overclock to 3.4ghz. It booted to the desktop without any issues. I loaded up Core Temp program and it displayed the CPU temperature in the mid-80s for all cores. I was surprised by the temperatures, but I thought maybe it's inaccurate. I decided to run Prime 95 and then temperatures skyrocket to 99C for all 4 cores. Prime 95 was still chugging along without any issues so I decide to go and clean one of my LCDs behind me. Then just out of the blue, the PC just shuts down. It literally powered off.

Initially, I thought maybe it was resetting because the system was unstable, but it really shut down. Nothing turned on as I waited 1 min. I pressed the power button, reaccessed the BIOS, go back to defaults, then booted to the desktop without any issues. I was relieved that nothing went bad. I decided to Prime 95 the machine at default settings just to make sure everything is ok and everything went without a hitch.

Hi, I also have a i5-750 and a Gigabyte motherboard. I had the same problem with high temperatures in overclocking over 3600 - 3800 MHz.
I am also interested to keep my computer alive for a long time that's why I stopped with it at 3320 Mhz and with low power consumption, as it is known that keeping your computer running at high voltages for everyday use, it greatly shorten it's life.

I Personnally could not get it past 3.83 ghz on my 750 / UD2. As I don't need such an overclock I got it back to 3.6ghz with power saving options enabled. but somehow my 750 did need voltage bump to reach clock speeds of 3.5/3.6 which disapointed me.